[webkit-dev] Terminology for giving up ownership: take, release, move

Ryosuke Niwa rniwa at webkit.org
Mon Sep 5 15:18:53 PDT 2016

On Mon, Sep 5, 2016 at 2:48 PM, Ryosuke Niwa <rniwa at webkit.org> wrote:
> On Mon, Sep 5, 2016 at 2:47 PM, Filip Pizlo <fpizlo at apple.com> wrote:
>> On Sep 5, 2016, at 2:35 PM, Ryosuke Niwa <rniwa at webkit.org> wrote:
>> On Mon, Sep 5, 2016 at 10:13 AM, Darin Adler <darin at apple.com> wrote:
>> Hi folks.
>> WebKit has some critical functions that involve asking an object to give up
>> ownership of something so the caller can take ownership.
>> In the C++ standard library itself, this is called move, as in std::move.
>> In WebKit smart pointers, we call this operation release, as in
>> RefPtr::releaseNonNull and String::releaseImpl.
>> In WebKit collections, we call this operation take, as in HashMap::take and
>> ExceptionOr::takeReturnValue.
>> The release vs. take terminology is distracting to my eyes. The verb “take"
>> states what the caller wishes to do, and the verb “release” states what the
>> caller wants the collection or smart pointer to do. My first thought was be
>> to rename the take functions to use the word release instead, but I fear it
>> might make them harder to understand instead of easier and clearly it would
>> make them longer.
>> I agree the verb "take" is not semantically sound here.  How about
>> HashMap::receiveReleased / ExceptionOr::receiveReleased?  Or simply
>> HashMap::released / ExceptionOr::takeReleased?  Even HashMap::receive
>> / ExceptionOr::receiveReturnValue might work better because "receive"
>> is more a passive form of accepting the ownership of something.
>> I don't think that HashMap::receiveReleased() fits with
>> Subject::verbPhrase().  In HashMap::take(), the HashMap is releasing
>> ownership of a value.  So, it is releasing it.  It's definitely not
>> receiving it.
> Oh I see.  Sorry, I had assumed they were just taking Ref<>&& as an
> argument.  In that case, release() definitely seems like the right
> terminology to use.

Hm... now that I recall the semantics of HashMap::take, I've started
to think that "release()" on its own may not be the right name for
collections because these member functions remove an item from a
collection while releasing the ownership.  Maybe "removeAndRelease()"
or "removeToRelease()" would do.

Alternatively, we could make the regular "remove()" always return the
removed value (or maybe this would result in more code bloat / runtime

- R. Niwa

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